Non-corrosive compositions comprising polymerized olefins prepared with certain catalyst metal compounds



United States Patent Ofiice 2,965,603 Patented Dec. 20, 1960NON-CORROSIVE COMPOSITIONS COMPRISING POLYMERIZED OLEFINS PREPARED WITHCERTAIN CATALYST METAL COMPOUNDS Charles Pfeifer, Midland, Mich.,assignor to The Dow Chemical Company, Midland, Mich., a corporation ofDelaware No Drawing. Filed Apr. 23, 1956, Ser. No. 579,753 8 Claims.(Cl. 260-45.7)

This invention relates to improved, non-corrosive compositions comprisedof select corrosion-inhibiting agents and polymerized olefinic and otherethylenically unsaturated materials which have been prepared withcertain catalytic metal compounds. In particular it relates tocompositions of this nature which are not corrosive or erosive to metalsand other materials of construction, particularly ferrous metals andalloys that do not have special corrosion-resisting properties and thatare susceptible to attack from hydrogen halides and like corrodents,especially at elevated temperatures. The invention also relates to amethod for preparing such compositions.

Various olefins and other ethylenically unsaturated materials,particularly ethylene, may be efiiciently polymerized, even asrelatively impure materials, to high molecular weight polymericcompounds at comparatively low pressures and temperatures, according toa process first proposed by Karl Zeigler and his associates in Germany.In this process, mixtures of strong reducing agents such as aluminumalkyls with compounds of group IVB, V-B, and VIB metals of the periodicsystem including thorium and uranium are employed as catalysts for thepolymerization. Polyethylenes, for example, having average apparentmolecular weights (as indicated by measurement of such characteristicsas their melt viscosities and the like) in excess of 40,000 and as largeas 100,000 to 3,000,000 can be manufactured by polymerizing ethylene gaswith such catalysts at temperatures beneath about 100 C. and underpressures less than about 100 atmospheres. It is frequently preferablewhen employing such catalysts according to the Zeigler process tooperate at temperatures of about 50 C. and under pressures be tweenabout 1 and 10 atmospheres. The reaction may suitably be conducted inthe presence of an organic liquid medium such as hexane, benzene,saturated petroleum hydrocarbon fractions and the like.

The polyethylenes prepared by the Zeigler process have superior andhighly desirable properties. For example, they may be made containingless than 3 and even less than 0.03 methyl groups per each 100 methylenegroups in the polymer molecule. The polymer molecules are practicallycompletely linear and are crystalline almost to their melting points,which usually are in the neighborhood of about 125-135 C. Theirdensities are commonly in the range of about 0.94-0.96 gram per cubiccentimeter and higher. They are insoluble in most solvents at ordinarytemperatures. Shaped articles formed with such polyethylenes have tearstrengths between about 1400 and 2800 pounds per square inch.Unstretched films prepared from them have tensile strengths in excess ofabout 2800 pounds per square inch and may be oriented by stretching topolyethylene film structures having tensile strengths as high as about42,500 pounds per square inch.

The strong reducing agents which advantageously are employed in thecatalyst mixtures of the Zeigler process include, among other compounds,a variety of aluminum trialkyls such as aluminum trimethyl, aluminumtriethyl, aluminum tripropyl, aluminum triisobutyl and higher aluminumtrialkyls as well as dialkyl aluminum halides, dialkyl aluminum hydridesand dialkyl aluminum alkoxides. Salts of metal selected from the groupconsisting of titanium, zirconium, uranium, thorium, vanadium andchromium are preferably employed as the group IV-B, V-B, and VI-Bmetallic compounds in the catalyst, although salts of the remainingmetals in these sub-groups may also be employed. Compounds of thesemetals including their halogenides, oxyhalogenides, complex halogenides,freshly precipitated oxides and hydroxides and such organic compounds asalcoholates, acetates, benzoates, acetyl acetonates and the like may beused in the catalyst.

A particularly active catalyst mixture for the Zeigler process may beobtained by mixing a titanium, zirconium or vanadium compound, such as atetrachloride, oxychloride or acetyl acetonate with an aluminum trialkylor a dialkyl aluminum compound. Generally, the molar quantities of thealuminum alkyl amployed to constitute the catalyst admixture are two tothree times the valence of the group IVB, VB, and VI-B metal compoundfor each mole of the latter compound which is present, although manyother ratios may also be employed satisfactorily. Amounts of thecatalyst admixture varying from 0.01 to a few percent by weight,depending on the degree of purity of the materials being polymerized,the desired rate of polymerization and the intended molecular weight,may suitably be employed.

After polymerization according to the Ziegler process, however,polyethylene and similar polymerized products contain residues from theadmixed metallic catalyst employed. The residues are not sufficientlyremoved by the conventionally utilized aftertreatment of polymericmaterials prepared accord ng to the Zeigler process. Such aftertreatmentusually involves fi'tration, preferably in the presence of air (whichtends to lighten the color of the product), to separate thepolymerization product from the reaction mass. This may be followed bysequential trituration with hexane, isopropanol, water, acetone andpentane prior to drying. When higher catalyst concentrations areemployed in the Ziegler process, some of the metallic compounds may beremoved from the polymeric product by extracting it with methanolichydrochloric acid, then washing it in methanol or acetone. Butanolwashings after the filtration in air have also been proposed todecompose and remove the catalyst residue.

It has been observed that the presence of certain catalyst residues inpolymeric materials prepared according to the Zie ler process tends toimpart decidedly undesirable characteristics to the polymers. Forexample, such polymers, particularly when the catalyst residue containshalogens. esneciallv chlorine, which may cause the presence of hydrogenhalides or like corrodents in the polymer, tend to be extremelycorrosive to most of the materials of construction commonly utilized inapparatus for extruding, shaping or molding the polymer. This is greatlypronounced in the frequent cases when the construction materialsemployed in such apparatus are particularly sensitive or susceptible toattack from hyhydrogen halides in the presence or absence of moisture,particularly hydrogen chloride. Many of the frequently employed ferrousmetals and alloys are susceptible to corrosive attack and cavitationalerosion of this nature, especially at elevated temperatures.

While various substances have been employed in other halogen-containingpolymeric materials to diminish their of or acting as receptors forhydrogen halides and the like which may be present or formed in thepolymer, many of these substances are not well suited for employmentwith polymeric materials, particularly polyethylene, prepared accordingto the Ziegler process. The reason for this is that a considerableproportion of the conventionally available substances tend to decomposeor become ineffective at the relatively high temperatures which arebeneficially employed for fabricating Ziegler type polymeric materials,particularly polyethylene. Fabricating temperatures in excess of about200 C. and frequently as high as 300 to 350 C. have been foundadvantageous for fabricating such polymers as polyethylene preparedaccording to the Ziegler process in order to obtain optimum physicalproperties in the fabricated polymeric article. In addition, many of theconventional corrosion-inhibiting substances tend to be toxic. Thisfurther lessens the desirability of their being employed in articlesintended for association with foodstuffs such as films, containers,cartons and the like.

It would be advantageous, therefore, to provide compositions preparedwith halogen-containing catalyst ad mixtures according to the Zieglerprocess and containing halogens in the catalyst residue which would benoncorrosive to materials that are susceptible to attack or cavitation,or both from hydrogen halides and like corrodents. It would beadditionally advantageous if such compositions were non-corrosive insuch a manner at elevated fabricating temperatures. It would beespecially advantageous if, besides being non-corrosive, many suchcompositions were non-toxic and adapted, for employment in articlesintended for association with foodstuffs or in other applicationswherein appreciable toxicity could not be tolerated.

These and other advantages and benefits may be realized according to thecompositions provided by the present invention which are comprised of apolymerized 'olefinic and other ethylenically unsaturated material,particularly polyethylene, prepared with halogen-containing catalystaccording to the herein described Ziegler process and containinghalogen-including residues from the catalyst which tend to cause thepresence of a hydrogen halide, particularly hydrogen chloride, or likecorrodent in the polymerized substance and a corrosion-inhibitingquantity of a salt compound of a monocarboxylic aliphatic acid radicalthat contains not more than 13 carbon atoms in its arrangement and ametal from group I-A of the periodic system which has a receptorfunction for and is capable of countereifecting hydrogen halide and likecorrodents. Ordinarily, the monocarboxylic aliphatic acid salt compoundmay advantageously be employed in the composition in an amount betweenabout 0.005 and 5 percent by weight, based on the weight of thecomposition. Frequently, in order to satisfactorily inhibit thecorrosive nature of many of the polymeric materials prepared accordingto the Ziegler process, an amount between about 0.5 and 2.0 percent byweight, based on the weight of the composition may be utilized. In allcases the relative amount of the monocarboxylic aliphatic acid saltcompound which will suitably inhibit corrosion can be predicated on therelative proportion of the halogen-including catalyst residue whichremains in the polymer product and the degree of the residues tendencyto cause the presence of a corrodent therein. Consideration of thesefactors under the influence of elevated temperatures must also beinvolved whenever fabrication of the corrosion-inhibited polymer at suchtemperatures is contemplated.

Compositions according to the present invention show little or notendency to corrode, erode or cause cavitation and chemical attack uponapparatus which may be employed for their fabrication, even when suchapparatus is constructed from such materials as mild steel and otherfrequently utilized ferrous metals and a loy hav'ng poor resistance tocorrosion from hydrogen halides, particularly hydrogen chloride, andlike corrodents. The inhibition of corrosion of the apparatus is alsoadvantageously obtained during fabrications at elevated temperatures.The compositions do not necessitate employing fabricating apparatuswhich is made from relatively more expensive materials of constructionwhich have special corrosion-resisting characteristics and eliminate theexpensive damage and waste which occurs when conventional apparatus iscorroded. In addition, better quality products may be obtained when thefabricating apparatus is kept free from the physical damage caused bycorrosion. Furthermore, a large proportion of the compositions arenon-toxic and may be employed safely with foodstuffs. In addition, manyof the corrosion-inhibitors according to the present invention enhancecertain other of the properties of the compositions, as for example,appearance, which may frequently be benefited by incorporation of acorrosion inhibitor having an ancillary pigmentation effect. Also, thegreat majority of the compositions of the present invention are tolerantof the presence of other conventional additament materials which may beemployed if required for such various purposes as to stabilize thecomposition against the effects of heat or light or oxygen to impartcolor or to attain other specific and desirable benefits.

Compounds selected from the monocar'boxylic aliphatic acid salts of thegroup I-A metals of the periodic system that contain 13 carbon atoms orless in their molecules may advantageously be employed ascorrosion-inhibitors in compositions according to the present inventionwith particular advantages being derivable when the metals are sodium orpotassium and the monocarboxylic aliphatic acid radical contains from 6to 10 carbon atoms. Such compounds may frequently cause less offensiveodors to be generated during their employment at high temperatures thanwhen lower acid radicals are involved and may also be found to be moreefficient corrosioninhibitors, on a quantity basis, than when salts ofhigher monocarboxylic aliphatic acid radicals are utilized.

In a series of illustrative examples, various corrosioninhibitingcompounds were incorporated in a relatively high molecular weightpolyethylene which was prepared with an admixed aluminum alkyl-titaniumtetrachloride catalyst according to the herein described Ziegler processand contained between about 0.02 and 0.08 percent by weight based on theweight of the polyethylene, of chloride in the catalyst residue. In eachof the tests a small plate of mild steel (1" x l x A") having a finishedsur' face was imbedded under compression molding within a particularpolyethylene sample in order to form a steelin-polymer matrix. Each ofthe test matrices was then maintained at a temperature of about 250 C.for about twelve hours after which it was cooled and stripped of thepolymer. Each of the test plates was permitted to remain overnight inair before being examined. The test plates were then inspected forevidences of corrosion. The following table reproduces the resultsobtained with several corrosion-inhibiting compounds.

Percent by wt. in polyethylene composition Compound Evidence ofcorrosion Sodium acetate Negligible.

None.

None. Negligible. None.

Do. Negligible.

Similar excellent results may be obtained with othercorrosion-inhibiting additament materials in accordance with theinvention.

The corrosiominhibiting compounds may be incorporated in compositionsaccording to the present invention in various suitable ways includingdry-blending the ingredients; mixing the ingredients on compoundingrolls and the like; and dispersing the corrosion-inhibiting compoundfrom liquid dispersion onto the polymer particles followed byevaporation of the liquid.

Since certain changes and modifications in the practice of the presentinvention can be entered into readily without departing substantiallyfrom its intended spirit and scope, it is to be fully understood thatall of the foregoing description and specification be interpreted asmerely being descriptive of certain of its preferred embodiments and notconstrued as being limiting or restrictive of the invention excepting asit is set forth and defined in the appended claims.

What is claimed:

1. Non-corrosive composition comprising polyethylcue-prepared bypolymerizing ethylene in the presence of a halogen-containing catalystformed by admixing (1) a strong reducing agent selected from the groupconsisting of aluminum trialkyls, dialkyl aluminum halides, dialkylaluminum hydrides and dialkyl aluminum alkoxides and (2) a compoundselected from the group consisting of halogenides, oxyhalogenides,complex halogenides, freshly precipitated oxides, freshly precipitatedhydroxides, alcoholates, acetates, benzoates and acetyl acetonates ofthe Group IV-B, V-B and VI-B metals of the Mendeleetf Periodic System,said polyethylene containing halogen-including catalyst residues afterhaving been polymerized which cause the presence of hydrogen halidecorrodents in the polymerized material and as a corrosion-inhibitor,between about 0.005 and 5 percent by weight of a satu ratedmonocarboxylic aliphatic acid radical that contains from 5 to carbonatoms in its arrangement and a metal from group I-A of the periodicsystem which has a receptor function for and is capable ofcountereffecting hydrogen halide and like corrodents.

2. The composition of claim 1 containing between about 0.5 and 2.0percent by weight of the corrosioninhibiting compound.

3. The composition of claim 1 wherein the corrosioninhibitor ispotassium pelargonate.

4. The composition of claim 1 wherein the corrosion inhibitor ispotassium caprylate.

5. The composition of claim 1 wherein the corrosioninhibitor ispotassium heptylate.

6. The composition of claim 1 wherein the corrosioninhibitor ispotassium caproate.

7. The composition of claim 1 wherein the corrosion inhibitor ispotassium valerate.

8. The composition of claim 1 wherein the polyethylene is prepared bypolymerizing ethylene in the presence of a catalyst formed by admixingan aluminum alkyl with titanium tetrachloride.

References Cited in the file of this patent UNITED STATES PATENTS2,181,478 Fligor Nov. 28, 1939 2,364,410 Whittaker Dec. 5, 19442,405,977 Peters Aug. 20, 1946 2,462,331 Meyers Feb. 24, 1949 2,507,142Chaban May 9, 1950 2,625,521 Fischer et al Jan. 13, 1953 2,734,892Carter Feb. 14, 1956 2,834,768 Friedlander May 13, 1958 2,838,477 Roelenet al June 10, 1958 2,843,577 Friedlander et al July 15, 1958 FOREIGNPATENTS 470,468 Canada Ian. 2, 1951 533,362 Belgium May 16, 1955 OTHERREFERENCES Pauling: General Chemistry; copyright 1947; published by W.H. Freeman & Co.

Partington: Test-book of Inorganic Chemistry, reprinted 1953, pub. byMacMillan and Co., London, pages 367 and 368.

Chemical Age Article, March 10, 1956, pp. 585 and 586.

1. NON-CORROSIVE COMPOSITION COMPRISING POLYETHYLENE-PREPARED BYPOLYMERIZING ETHYLENE IN THE PRESENCE OF A HALOGEN-CONTAINING CATALYSTFORMED BY ADMIXING (1) A STRONG REDUCING AGENT SELECTED FROM THE GROUPCONSISTING OF ALUMINUM TRIALKYLS, DIALKYL ALUMINUM HALIDES, DIALKYLALUMINUM HYDRIDES AND DIALKYL ALUMINUM ALKOXIDES AND (2) A COMPOUNDSELECTED FROM THE GROUP CONSISTING OF HALOGENIDES, OXYHALOGENIDES,COMPLEX HALOGENIDES, FRESHLY PRECIPITATED OXIDES, FRESHLY PRECIPITATEDHYDROXIDES, FRESHLY HOLATES, ACETATES, BENZOATES AND ACETYL ACETONATESOF THE GROUP IV-B, V-B AND VI-B METALS OF THE MENDELEEFF PERIODICSYSTEM, SAID POLYETHYLENE CONTAINING HALOGEN-INCLUDING CATALYST RESIDUESAFTER HAVING BEEN POLYMERIZED WHICH CAUSE THE PRESENCE OF HYDROGENHALIDE CORRODENTS IN THE POLYMERIZED MATERIAL AND AS ACORROSION-INHIBITOR, BETWEEN ABOUT 0.005 AND 5 PERCENT BY WEIGHT OF ASATURATED MONOCARBOXYLIC ALIPHATIC ACID RADICAL THAT CONTAINS FROM 5 TO10 CARBON ATOMS IN ITS ARRANGEMENT AND A METAL FROM GROUP I-A OF THEPERIODIC SYSTEM WHICH HAS A RECEPTOR FUNCTION FOR AND IS CAPABLE OFCOUNTEREFFECTING HYDROGEN HALIDE AND LIKE CORRODENTS.